1. Field of the Invention
The invention relates to a textile machine monitor which applies several methods of electronic processing to signals received from a thread feed sensor.
2. Description of Related Art
a. Thread Monitors
The prior art includes a variety of mechanical and electrical devices for monitoring and controlling textile equipment. The present invention adds a number of capabilities that are not addressed in the prior art.
A common thread/yarn monitor employs a mercury switch device which maintains an open circuit condition while the thread/yarn is under tension at the switch location. In the event the thread breaks, a closed circuit results indicating the breakage.
Electronic thread motion sensor devices utilized in the prior art, such as described in U.S. Pat. No.4,429,651, (Tajima), includes a motion/no motion sensor wherein a fault/break is indicated when "no motion" is detected when "motion" is required. The current invention can act prior to thread break, which can prevent: 1) damage to the finished product resulting from snags or mechanical failures which occur prior to a thread break; 2) damage to machines which can occur prior to a thread break, for example, when large amounts of thread wrap on the take-up cam shaft; and 3) waste of time and thread when operators of automatic machines monitor and remove thread spools before exhaustion in order to prevent a break at the end of the spool.
Much of the prior art is limited to tension sensing/analysis, but electronic tension sensing/analysis can address only limited and specific issues. Such prior art includes: U.S. Pat. No. 5,237,944 to Willenbacher, et al.; U.S. Pat. No. 4,628,847 to Rydborn; and, U.S. Pat. No. 4,763,588 to Rydborn. U.S. Pat. No. 5,237,944 to Willenbacher, et al., in fact states that "[m]easurement experiments have shown that such parameters as the speed of sewing, stitch length, and the thread properties cause only insignificant changes in the maximum of the voltage peaks, whereas the setting of the tensioning device substantially affects it." U.S. Pat. No. 5,237,944 is directed to the analysis of tension changes that are generated by take up type elements of a sewing machine. That invention, however, also requires input feedback from a machine shaft position sensor and detects only a specific input signal pattern for a designated machine type. Changes in machine type or take-up structure would require fundamental design changes to the invention. The present invention provides for an analysis on all textile machine types and requires no machine retrofit.
U.S. Pat. No. 4,110,654, issued to Andreas Paul, describes a sensor wherein a member vibrates when excited by a traveling yarn. That invention, however, does not include a signal processing means. In addition, the vibration frequency of the vibrating member is affected by the attachment of piezo type devices to the vibrating member. Failure to match a precise vibrating frequency to requirements can produce a high signal to noise ratio. While vibration isolation and vibration frequency differences of vibrating member and a base are determined in U.S. Pat. No. 4,110,654, there is no provision for these factors for upstream or downstream thread guides. Also, that invention suggests an enclosure to contain the effect of airborne noise, but, a mechanical enclosure may result in compaction of dust. The vibration means of the present invention is relatively insensitive to air noise, due to its low mass, small cross sectional area made possible by its simple design and to the independent, non-machine mounting of sensor assembly.
U.S. Pat. No. 4,381,803 issued to Weidmann, et al., is primarily directed to determining tension in weaving machines at various stages of weft insertion. That invention includes a motion responsive member consisting of a piezoelectrical system set into vibration by filament movement. The piezo element itself, however, can impact the vibration frequency, and the sensor does not control or define vibration frequency. In addition, the electronic circuit is not frequency filtered/tuned. The sensor signal amplitude is compared to fixed/set values in order to generate rectangular pulses, which are then matched to the machine via a rotating disk affixed to the machine. Also, no provision is made to control dust compaction.
U.S. Pat. No. 4,619,213 (Iimura, et al.), measures thread draw during stitch formation by wrapping thread on a pulley and sensing the rotation of the pulley. Angular momentum of the pulley prevents detection of rapid start and stop thread movement generated by textile machine take up action and stitch formation. The present invention, on the other hand, determines draw as a function of thread sensor signal and time.
U.S. Pat. No. 4,566,319 (Yamazaki, et al), entitled "PROCESS AND APPARATUS FOR MEASURING THERMAL SHRINKAGE PROPERTIES OF YARN" and U.S. Pat. No. 5,146,739 (Hellmut Lorenz) entitled "YARN FALSE TWIST TEXTURING PROCESS AND APPARATUS", both describe devices for monitoring various criteria, including, the tension of thread or yarn to detect abnormal characteristics such as "false twisting" and shrinkage. The Yamazaki device uses pulleys to determine speed. As in U.S. Pat. No. 4,619,213, above, angular momentum imposes limits to speed change sensitivity. In addition, neither device detects the presence of a knot or the like.
U.S. Pat. No. 3,058,343 (G. H. Hutchens, et al.) entitled "APPARATUS FOR MONITORING YARN SURFACE DEFECTS", and U.S. Pat. No. 2,881,833 (J. M. Hoffee) entitled "SEWING MACHINE ATTACHMENT FOR CUTTING SEAM BINDING" are of general interest only in that they disclose devices for monitoring and/or cutting threads or fabrics employed in textile production.
Prior literature also describes commercially available systems for monitoring the delivery of threaded yarn. Several such systems are produced and sold by Eltex of Sweden, Inc., Greer, S.C. In such systems, a hole, or eyelet, which may include a piezoelectric element, detects the presence or absence of thread or yarn.
There are combined commercial thread cutters and detectors available on the market such as those available from Fli Control and sold by Wilson Controls & Meters Co., Inc., Harrisburg, N.C. 28075.
Prior art sensors do not have specific means to sense knots and material inconsistencies, nor are they directed to speed sensitivity. Likewise, prior art electronic processing generally does not include means to determine or predict operating status based on average or trend changes for a multiplicity of duty cycles (stitches). The prior electronic processing art generally does not identify a time arid signal magnitude pattern generated by thread take up for a singular stitch/duty cycle based on sensed thread/fabric speed. Moreover, the prior art does not generate a numerical or voltage value which is a combined function of duty cycle time plus speed parameters for a (singular) duty cycle/stitch. In addition, the prior art generally does not address automatic machine diagnosis based on thread sensor input. U.S. Pat. No. 5,388,618, (Decock) for example, uses operator supplied input for machine diagnosis. The prior art does not address stitch count/production accounting using thread/fabric sensor output. The prior art does not produce an accurate measure of fabric processed wherein measure is derived from output of a thread sensor. Lastly, the prior art does not provide means to detect burrs on needles.
In detail, among the advantages provided by the sensor in the present invention over prior art sensors is that: 1) speed as well as tension is sensed, such that speed sensitivity is combined with electronic analysis revealing aspects of machine operation that are unavailable from the cited systems; and 2) unlike the patent disclosures cited herein, the present invention provides for controlled sensing of knots and fiber inconsistencies. Acceptable knot/inconsistency dimensions are set by sensor design.
The current electronic processor indicates and predicts malfunctions via several unique signal processing methods. The methods include: 1) use of signal magnitude comparison plus rate of change (derivative function) which allows simple enhanced identification of inconsistencies such as knots and filament inconsistency, and identification of burred needles from appropriate thread sensor input; 2) use of thread sensor output to identify thread time and speed patterns for a singular stitch/duty cycle. Control values (voltage or numerical) that are a function of combined amplitude and time parameters permit simple identification of operational change or malfunction for general machine types. User adjustment/input to the function of speed or time allows easy application of the present embodiment to any textile process; 3) determination of long term average sensor signal (which is equivalent to average speed) for a multiplicity of duty cycles/stitches which, in turn, provide for analysis of small changes and trends. This combination of speed and time allows for the determination of operation status, using thread drawn in during a given period of time. In addition, for adjustment the averaging time period is shortened, it is gradually increased after start up, and the upper and lower limits used to compare with the average gradually converge after start up.
The use of sensor and signal processing in the current embodiment allows this monitor to be moved from one type of machine to another without requiring machine retrofit. In addition, elements of this invention can be used separately or together on many different types of textile machines. The present invention comprises a low or zero tension device. The sensor, by not requiring or exerting tension, is transparent to the machine being monitored. Low tension is especially useful for elastic fiber such as textured polyester. Moreover, low tension permits mounting of the detector anywhere between thread spool and the machine.
The cited patent literature discloses threading via closed orifices such as eyelets. In contrast, the present invention allows simple threading via open sided, ladder type, guides. Threading can easily and quickly be accomplished with no break in thread and no visual input.
The present invention is an essentially self-cleaning device and, therefore, is resistant to problems caused by compaction of dust. Several of the devices disclosed in the cited patents would require regular removal of dust for proper operation.
As a consequence of its sensitivity, the present invention has made provision for vibration isolation and resonant frequency mismatch of relevant components, including guides and base.
b. Fabric Monitors
A typical, prior art material/fabric monitor system involves placement of textile material between electrical contacts. When the material runs out, the contacts close a circuit. This approach, however, cannot detect feed problems such as snags. In addition, contacts can be fouled by dust and fibers.
U.S. Pat. No. 3,177,749 (K. J. Best, et al.), teaches a control for feeding, measuring and cutting strip material wherein a wheel having a plurality of apertures disposed therethrough interrupts a light source which is focused on a light sensitive element. This counter wheel makes contact with the material passing through the apparatus through the use of a pressure wheel which sandwiches the material between the pressure wheel and the counter wheel. This and other related devices require that tension/friction be applied to material. The tension/friction requirement limits some applications, especially the feeding of elastic material. In addition, these devices have limits on response time due to the momentum of moving parts. Such devices are subject to fouling by material inconsistency, snags and dust contamination, and are also limited to measuring length.
U.S. Pat. No. 4,286,487 entitled "APPARATUS FOR MONITORING THE DELIVERY OF MATERIAL" issued to L. P. Rubel, the inventor of the device disclosed herein, discloses an apparatus for monitoring the unwinding of a length of material from a spool, wherein the turning of a shaft which mounts the spool generates a pulsed electric signal for controlling a device. The apparatus detects whether fabric from a spool is tangled, snarled, or otherwise jammed or consumed. This apparatus is limited in response time by the angular momentum of the spool being monitored.
Unlike the cited monitor devices, the current monitor response time is a function of the frequency of vibration of a vibrating means. Moreover, the frequency of vibration can be designed to requirements. High speed operation and sensitivity to variations in speed, tension, snags, knots and inconsistencies of moving material and resultant sensitivity to duty cycle of the machine being monitored makes possible the response to an array of fault modes and prediction of fault prior to damage. Response can be expanded to machine diagnosis and accounting.